The present invention relates to a nucleus medical diagnosis system, and, more particularly, to an improvement in data processing for obtaining a preferable diagnostic image in a digital scintillation camera system.
When some radioactive drugs, i.e., drugs containing RI's (radioisotopes) are administered (e.g., injected into a blood vessel), they tend to concentrate in specific areas (e.g., a tumor or the like in an internal organ) of a patient's body. Consequently, the distribution of the drug in the patient can be externally detected through detection of the RI contained in the drug, the detected distribution being used for subsequent diagnosis.
A scintillation camera system is known as a conventional radioactive diagnosis apparatus. In the conventional scintillation camera system, a diagnostic image (i.e., an RI distribution image) of the patient is formed on a film, e.g., an X-ray film Incident positions of gamma rays sequentially emitted from an object injected with a radioactive drug are detected by the scintillation camera which then generates corresponding position signals. Light from the scintillator, upon reception of the gamma ray, is detected by a plurality of photosensors such as PMTs (photomultiplier tubes). By utilizing detection signals from the PMTs, the incident position of the gamma ray can be calculated. A gamma-ray incident position signal from the scintillation camera is supplied to the imaging apparatus of the scintillation camera (hereinafter called a "gamma imager"). The gamma imager drives a CRT (cathode-ray tube) to turn on a dot corresponding to the incident position in response to the incident position signal. The bright dot is exposed on a film such as an X-ray film. Bright dots are exposed on the film for a predetermined period of time, thereby providing an RI distribution image.
Digital scintillation camera systems have become widespread in recent years. In the conventional digital scintillation camera system, a position signal from the scintillation camera system is digitized, and a count of a pixel corresponding to an image memory is incremented in response to the position data, so that gamma-ray incident data are accumulated in the image memory. The image data stored in the memory represents RI distribution data obtained by counts representing the number of times of gamma-ray incidence for each pixel within a predetermined period of time. The image data stored in the memory is converted to a video signal representing a grey-level corresponding to the count. The video signal is displayed and supplied to a video imager. An RI distribution image from the patient is formed on a film (e.g., an X-ray film) in response to the input video signal.
The relationship between the gamma-ray count and the density of X-ray films (hereinafter called "count-density characteristics") is shown in FIG. 1. The pictures of the X-ray films were obtained by a conventional nondigital scintillation camera system (to be referred to as an analog scintillation camera system hereinafter so as to distinguish it from the digital scintillation camera system) and a digital scintillation camera system.
Referring to FIG. 1, the count is plotted along the abscissa and the density is plotted along the ordinate. As shown in FIG. 1, a characteristic curve P0 is given as a solid curve of an RI distribution image formed on an X-ray film by a gamma imager in an analog scintillation camera system, and a characteristic curve P1 is given as a broken curve of an RI distribution image formed on an X-ray film by a video imager in a digital scintillation camera system. The count-density characteristics of the analog and digital scintillation camera systems, with respect to the X-ray film, differ from each other. Therefore, even if data can be acquired under the same conditions, diagnostic images (RI distribution images) having different grey-level characteristics, i.e., density characteristics are formed on the respective X-ray films. For this reason, diagnosticians (i.e., a doctor) accustomed to a conventional analog scintillation camera system feel uneasy in operating a digital scintillation camera system. As a result, diagnosis cannot be easily performed, resulting in inconvenience.
The count-density characteristics are preferably represented by a line (count in proportion with density) different from the lines indicating characteristic curves P0 and P1, in order to allow correct display and recognition of the RI distribution. However, an image having a linear correlation between the count and the density may not be easy to recognize for an operator who is accustomed to a conventional analog scintillation camera system. Nonetheless, an image having a linear correlation between count and density is considered as the best means of expressing an RI distribution. Such an image is, in fact, expected to become the standard RI distribution image.
Count-density characteristics obtained by the digital scintillation camera system differ from those of the conventional analog scintillation camera system and from those of a system wherein a linear correlation between the count and the density is obtained. The count-density characteristics of the diagnostic image provided via the present digital scintillation camera system are, therefore, inapplicable to practical applications. Moreover, the count-density characteristics are mainly determined by exposure characteristics of the film by the video imager, and cannot be easily modified.